ASSAYING. 
the integer, and whatever he its real weight 
it is denominated the assay pound. This 
imaginary pound is then subdivided into 
aliquot parts, but differing according to the 
metal. The silver assay pound is subdivid- 
ed into 12 imaginary ounces, each ounce 
into 20 pennyweights ; and, for assaying, 
these again into halves. 
The following is the table of the propor- 
tions of lead required to different alloys of 
copper. In the three first columns is shewn 
the absolute increase of the quantity of 
lead in alloys of decreasing fineness. In the 
three lust columns wall be seen the gradual 
diminution of the protecting power of fine 
metal against scorification, in proportion to 
the increase of alloy, shewn by the decreas- 
ing quantity of lead required for the same 
weight of copper, under different mix- 
tures. 
Silver. Copper. 
23 with 1 requires 
22 2 
20 4 
18 6 
16 8 
14 10 
12 12 
10 14 .. 
8 16 
6 18 
4 20 
2 22 
Lead. Ratio of Inc. Copper. Silver. _ Lead 
96 = 4 X 24 and hence 1 with 23 requires 96 
144= 6 X 24 1 11 72 
192= 8 X 24 . 1 5 
240 = 10 X 24 1 3 40 
288 = 12 X 24 1 2 36 
336 = 14 X 24 1 If 33 
384 = 16 X 24 1 1 32 
432 = 18 X 24 1 | 30 
480 = 20 X 24 1 § 30 
. 528 = 22 X ^4 1 a 29 
. 576 = 24 X 24 1 i 28 
.624 = 26 X 24.. 1 ...... A 28 
It should be remarked, however, that 
many assayers, of good authority, use pro- 
portions of lead to alloy considerably differ- 
ent from the above table ; and that the 
whole numbers here given may be consider- 
ed as rather high in proportion to the quan- 
tity of lead. 
The proportions of lead for gold assaying 
are nearly the same as for silver. 
Assays of alloys with platina are con- 
ducted nearly in the same manner as for 
the mixtures of silver and gold. Silver is 
seldom alloyed with it ; but gold is more 
frequently ; and is known by the much 
greater heat it requires in the fusion ; by the 
edges of the button appearing thicker and 
rounder than in common assays of gold ; by 
its colour being duller and tending to yel- 
low ; and its being entirely crystallised on 
it surface. 
The action of nitrons acid on the alloys of 
platina is very remarkable. By itself, pla- 
tina is as insoluble in this acid as gold, and 
a mixture of these two metals equally resists 
its action ; but when silver enters into the 
mixture in the proportion of t\, or three 
times the weight of the gold and platina, 
and when the platina is not above a tenth 
of the gold, the platina is totally soluble in 
nitrous acid, together with the silver, and 
the gold alone remains untouched. 
When the gold mixed with platina is to 
he freed from it in the above manner, it 
saust be laminated very thin ; a weak acid 
is first added and boiled for some time. If 
the platina is above two per cent, of the 
gold, the acid assumes a straw colour, which 
deepens in proportion to the platina, and at 
the same time the cornets assume a brownish 
green. A stronger acid is then added, and 
boiled three times successively, to detach 
the last portions of platina which are sepa- 
rated with difficulty. By laminating very 
fine, using the acid liberally, and long boil- 
ing, all the platina may be separated in one 
operation, when it doesxnot exceed a tenth 
of the gold: and above that proportion the 
colour of the gold is so much debased, and 
the appearances on the cupel so striking, 
that fraud can hardly escape an experienced 
eye. Parting might be used even when the 
platina was more than a tenth of the gold, 
but then more silver must be added, whicii 
would render the cornet so very thin after 
the action of the acid that it could hardly 
be annealed without breaking. 
When alloys of silver alone with platina 
are treated with nitrous acid, the silver dis- 
solves as usual, hut the liquor soon becomes 
muddy with a very fine bulky black pre- 
cipitate, which continues increasing till all 
the silver is dissolved, and which is found 
to be entirely platina when collected. A 
part of the platina, however, remains in the 
solution, for on adding muriatic acid to the 
liquor separated from the black precipitate, 
white Inna cornea falls down, after which 
carbonate of potash will throw down a green 
C c 2 
